Magnetic tape media comprises a medium for storing large amounts of data, and typically comprises a plurality of data tracks that extend longitudinally along the tape. A tape head is employed for reading and/or writing data on the data tracks, and is typically shared between various data tracks or groups of data tracks, and is moved between tracks or groups of tracks in the lateral direction of the tape. The tape head typically comprises a number of separate elements which read and/or write data with respect to a number of parallel data tracks, and is associated with one or more separate servo read heads, which are laterally offset from the read and/or write elements, so as to track follow a servo band and be guided along the data track or tracks. A servo band provides the servo guidance along any of several paths within the band, and the tape head is repositioned laterally within a servo band so that the read and/or write elements access different data tracks. The servo bands are continuous to provide constant track following. Incorporated U.S. Pat. No. 5,689,384 provides timing based servo bands to allow for track following for each of a number of paths across the servo band.
The lateral positioning of the tape head is typically accomplished by actuators, which may have mechanical or electromechanical components. The servo read head is smaller than the lateral width of the servo band, and once the proper lateral positioning of the tape head has been accomplished, as the servo information being sensed by the servo read head indicates, minor adjustments of the head to follow a particular path within the servo band is made by lateral movement of the tape or of the tracks on the tape. Similarly, lateral repositioning of the tape head to different tracks within the same servo band is accomplished by an adjustment of position within the servo band to another path.
The track following is based on the servo signal as read by the servo read head. Timing based servo systems compare the time between peaks to derive the servo read head lateral position. Therefore, the timing based position error signal (PES) is insensitive to speed of the magnetic tape and insensitive to the amplitude of the servo pattern on the magnetic tape. However, noise (tape or electronics) and signal dropout due to media defects can corrupt and cause missed peaks. Additionally, asymmetry (readback distortion), a result of reading with magneto-resistive servo read heads, can in turn reduce peak detection margin, and result in missed peaks.